U.S. patent application number 13/598759 was filed with the patent office on 2013-02-21 for mri safe actuator for implantable floating mass transducer.
This patent application is currently assigned to VIBRANT MED-EL HEARING TECHNOLOGY GMBH. The applicant listed for this patent is Wolfgang Amrhein, Geoffrey Ball, Peter Lampacher, Gunther Weidenholzer. Invention is credited to Wolfgang Amrhein, Geoffrey Ball, Peter Lampacher, Gunther Weidenholzer.
Application Number | 20130046131 13/598759 |
Document ID | / |
Family ID | 41650097 |
Filed Date | 2013-02-21 |
United States Patent
Application |
20130046131 |
Kind Code |
A1 |
Ball; Geoffrey ; et
al. |
February 21, 2013 |
MRI Safe Actuator for Implantable Floating Mass Transducer
Abstract
An implantable hearing prosthesis for a recipient patient is
described. An implantable signal transducer includes one or more
electromagnetic drive coils for receiving an electrical stimulation
signal and a cylindrical transducer magnet arrangement including an
inner disk magnet having a first magnetic field direction, and an
outer annular magnet surrounding the inner rod magnet and having a
second magnetic field direction opposite to the first magnetic
field direction. Current flow through the one or more
electromagnetic drive coils from the electrical stimulation signal
creates a coil magnetic field that interacts with the magnetic
fields of the transducer magnet arrangement to create vibration in
the transducer magnet which is developed by the signal transducer
as a mechanical stimulation signal for audio perception by the
patient.
Inventors: |
Ball; Geoffrey; (Axams,
AT) ; Lampacher; Peter; (Innsbruck, AT) ;
Amrhein; Wolfgang; (Ottensheim, AT) ; Weidenholzer;
Gunther; (Ottensheim, AT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ball; Geoffrey
Lampacher; Peter
Amrhein; Wolfgang
Weidenholzer; Gunther |
Axams
Innsbruck
Ottensheim
Ottensheim |
|
AT
AT
AT
AT |
|
|
Assignee: |
VIBRANT MED-EL HEARING TECHNOLOGY
GMBH
Innsbruck
AT
|
Family ID: |
41650097 |
Appl. No.: |
13/598759 |
Filed: |
August 30, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12634940 |
Dec 10, 2009 |
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13598759 |
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61121399 |
Dec 10, 2008 |
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61227603 |
Jul 22, 2009 |
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61263150 |
Nov 20, 2009 |
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Current U.S.
Class: |
600/25 |
Current CPC
Class: |
H04R 2460/13 20130101;
H04R 2225/67 20130101; H04R 25/606 20130101 |
Class at
Publication: |
600/25 |
International
Class: |
H04R 25/02 20060101
H04R025/02; A61F 11/04 20060101 A61F011/04 |
Claims
1. An implantable hearing prosthesis for a recipient patient, the
prosthesis comprising: a receiving coil for transcutaneous
receiving of an externally generated communication signal; an
implantable signal processor in communication with the receiving
coil for converting the communication signal into an electrical
stimulation signal; an implantable signal transducer in
communication with the signal processor and including: i. one or
more electromagnetic drive coils for receiving the electrical
stimulation signal; ii. a cylindrical transducer magnet arrangement
including an inner disk magnet having a first magnetic field
direction, and an outer annular magnet surrounding the inner rod
magnet and having a second magnetic field direction opposite to the
first magnetic field direction; wherein current flow through the
one or more electromagnetic drive coils from the electrical
stimulation signal creates a coil magnetic field that interacts
with the magnetic fields of the transducer magnet arrangement to
create vibration in the transducer magnet which is developed by the
signal transducer as a mechanical stimulation signal for audio
perception by the patient.
2. A prosthesis according to claim 1, wherein the signal transducer
includes a hermetically sealed transducer housing.
3. A prosthesis according to claim 2, wherein the transducer
housing is sealed by a silicone elastomer.
4. A prosthesis according to claim 2, wherein the transducer
housing is made of titanium.
5. A prosthesis according to claim 1, wherein the prosthesis is a
middle ear implant device.
Description
[0001] This application is a divisional of U.S. patent application
Ser. No. 12/634,940, filed Dec. 10, 2009, which in turn claims
priority from U.S. Provisional Patent Application 61/263,150, filed
Nov. 20, 2009, and from U.S. Provisional Patent Application
61/227,603, filed Jul. 22, 2009, and from U.S. Provisional Patent
Application 61/121,399, filed Dec. 10, 2008, all of which are
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to medical implants, and more
specifically to a novel bone conduction transducer for an
implantable hearing prosthesis.
BACKGROUND ART
[0003] A normal ear transmits sounds as shown in FIG. 1 through the
outer ear 101 to the tympanic membrane (eardrum) 102, which moves
the ossicles of the middle ear 103 (malleus, incus, and stapes)
that vibrate the oval window and round window openings of the
cochlea 104. The cochlea 104 is a long narrow organ wound spirally
about its axis for approximately two and a half turns. It includes
an upper channel known as the scala vestibuli and a lower channel
known as the scala tympani, which are connected by the cochlear
duct. The cochlea 104 forms an upright spiraling cone with a center
called the modiolar where the spiral ganglion cells of the acoustic
nerve 113 reside. In response to received sounds transmitted by the
middle ear 103, the fluid-filled cochlea 104 functions as a
transducer to generate electric pulses which are transmitted to the
cochlear nerve 113, and ultimately to the brain.
[0004] Hearing is impaired when there are problems in the ability
to transduce external sounds into meaningful action potentials
along the neural substrate of the cochlea 104. To improve impaired
hearing, various types of hearing prostheses have been developed.
For example, when hearing impairment is associated with the cochlea
104, a cochlear implant with an implanted stimulation electrode can
electrically stimulate auditory nerve tissue within the cochlea 104
with small currents delivered by multiple electrode contacts
distributed along the electrode. FIG. 1 also shows some components
of a typical cochlear implant system which includes an external
microphone that provides audio information to an external signal
processor 111 where various signal processing schemes can be
implemented. The processed data communications signal with the
audio information is then converted into a digital data format,
such as a sequence of data frames, for transcutaneous transmission
by an external transmitting coil 107 to a corresponding receiving
coil in an implant processor 108. Besides extracting the audio
information from the data communications signal, the implant
processor 108 also performs additional signal processing such as
error correction, pulse formation, etc., and produces a stimulation
pattern (based on the extracted audio information) that is sent
through an electrode lead 109 to an implanted electrode array 110.
Typically, this electrode array 110 includes multiple electrodes on
its surface that provide selective stimulation of the cochlea
104.
[0005] When hearing impairment is related to operation of the
middle ear 103, a conventional hearing aid may be used to provide
acoustic-mechanical vibration to the auditory system. With
conventional hearing aids, a microphone detects sound which is
amplified and transmitted in the form of acoustical energy by a
speaker or another type of transducer into the middle ear 103 by
way of the tympanic membrane 102. Interaction between the
microphone and the speaker can sometimes cause an annoying and
painful a high-pitched feedback whistle. The amplified sound
produced by conventional hearing aids also normally includes a
significant amount of distortion.
[0006] Efforts have been made to eliminate the feedback and
distortion problems using middle ear implants that employ
electromagnetic transducers. A coil winding is held stationary by
attachment to a non-vibrating structure within the middle ear 103
and microphone signal current is delivered to the coil winding to
generate an electromagnetic field. A magnet is attached to an
ossicle within the middle ear 103 so that the magnetic field of the
magnet interacts with the magnetic field of the coil. The magnet
vibrates in response to the interaction of the magnetic fields,
causing vibration of the bones of the middle ear 103. See U.S. Pat.
No. 6,190,305, which is incorporated herein by reference.
[0007] Middle ear implants using electromagnetic transducers can
present some problems. Many are installed using complex surgical
procedures which present the usual risks associated with major
surgery and which also require disarticulating (disconnecting) one
or more of the bones of the middle ear 103. Disarticulation
deprives the patient of any residual hearing he or she may have had
prior to surgery, placing the patient in a worsened position if the
implanted device is later found to be ineffective in improving the
patient's hearing.
[0008] U.S. Patent Publication 20070191673 and U. S. Provisional
Patent Application 61/121,399, filed Dec. 10, 2008, which are
incorporated herein by reference, describe driving a relatively
large inertial mass to vibrate the skull bone of a hearing impaired
patient. As shown in FIG. 2, a floating mass transducer (FMT) 203
is mechanically connected to the temporal bone of the patient. The
mass of the floating mass transducer (FMT) 203 vibrates in response
to the audio information in a data communications signal
originating from an external processor 201 and transmitted to an
implanted receiving coil 202. Bone conduction of the FMT vibrations
through the temporal bone are transduced into fluid motion within
the cochlea and perceived as sound.
SUMMARY OF THE INVENTION
[0009] Embodiments of the present invention include an implantable
hearing prosthesis for a recipient patient. An implantable signal
processor is in communication with the receiving coil and converts
the communication signal into an electrical stimulation signal. An
implantable signal transducer is in communication with the signal
processor and includes one or more electromagnetic drive coils for
receiving the electrical stimulation signal and a cylindrical
transducer magnet arrangement including an inner disk magnet having
a first magnetic field direction, and an outer annular magnet
surrounding the inner rod magnet and having a second magnetic field
direction opposite to the first magnetic field direction. Current
flow through the one or more electromagnetic drive coils from the
electrical stimulation signal creates a coil magnetic field that
interacts with the magnetic fields of the transducer magnet
arrangement to create vibration in the transducer magnet which is
developed by the signal transducer as a mechanical stimulation
signal for audio perception by the patient.
[0010] In some embodiments, the signal transducer may include a
hermetically sealed transducer housing, which may be sealed by a
silicone elastomer and/or may be made of titanium. And the
prosthesis may be a middle ear implant device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 shows structures of a typical ear which includes a
cochlear implant.
[0012] FIG. 2 illustrates the operating principle of a bone
conduction prosthesis.
[0013] FIG. 3 shows an example of a prior art bone conduction
prosthesis.
[0014] FIG. 4 shows an example of an implantable hearing prosthesis
according to an embodiment of the present invention.
[0015] FIG. 5 shows various structural details of a transducer
according to one embodiment of the present invention.
[0016] FIG. 6A-C shows various views of a bone conducting
transducer according to one specific embodiment of the present
invention based on a piezoelectric inertial mass arrangement.
[0017] FIG. 7 shows A-E shows various views of a bone conducting
transducer according to one specific embodiment of the present
invention based on an arrangement of one or more electromagnetic
coils that interact with a permanent magnet inertial mass.
[0018] FIG. 8A-C shows various details of an embodiment having an
easily insertable and removable drive transducer.
[0019] FIG. 9A-C shows details of a surgical procedure for
inserting an embodiment such as the one shown in FIG. 8.
[0020] FIG. 10A-C shows various alternative structural details
according to specific embodiments.
[0021] FIG. 11A-B shows different height transducer housings
according to different embodiments.
[0022] FIG. 12A-C shows structural details of embodiments based on
piezoelectric elements.
[0023] FIG. 13A-B shows various structural details of en
electromagnetic drive coil according to an embodiment.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
[0024] FIG. 3 shows elements of an implantable hearing prosthesis
as described, for example, in U.S. Patent Publication 20070191673
("Ball '673"), which is based on driving a relatively large mass to
vibrate the skull bone of a hearing impaired patient. Bone
conduction of these vibrations is transduced into fluidic vibration
within the cochlea that is sensed by the patient as sound. More
specifically, FIG. 3A shows a top plan view and FIG. 3B shows a
side cross-section view of an implantable hearing prosthesis 300
using an inertial mass-based bone conduction transducer. A silicone
elastomer receiver housing 301 contains a receiving coil 302 that
transcutaneously receives communications signals from the external
audio processor, and a holding magnet 303 that cooperates with a
corresponding external magnet to hold the external audio processor
in correct position over the receiving coil 302. An implant signal
processor 304 receives the communications signals from the
receiving coil 302 and produces a corresponding electrical
stimulation signal to a bone conduction transducer 305,
specifically, a dual opposing magnet type floating mass transducer
(FMT), which is enclosed in a titanium transducer housing 306.
Mounting of the transducer housing 306 to the skull bone is
accomplished by multiple pairs of attachment ears 307 which are
surgically mounted to the bone with connecting screws. The FMT mass
of the bone conduction transducer 305 vibrates in response to the
electrical stimulation signal from the implant signal processor
304, which in turn causes inertial vibration of the transducer
housing 306. The housing vibrations are transduced through the
temporal bone by bone conduction into fluid motion within the
cochlea and perceived as sound.
[0025] While an improvement in the field, the implantable hearing
prosthesis 300 of Ball '673 is not without issues. For example, the
Ball '673 implantable hearing prosthesis 300 has multiple mounting
holes which require a high degree of planarity in the bone
surrounding the implantation site. And the Ball '673 implantable
hearing prosthesis 300 is configured such that in a relaxed state,
the receiver housing 301 and the transducer housing 306 are biased
to lie in a single plane. Thus, when implanted onto the curved
skull bone of a recipient patient, this existing bias exerts a
force that tends to pull the two housings back into a common plane,
away from the curvature of the underlying skull bone.
[0026] Embodiments of the present invention are directed to an
implantable bone conduction hearing prosthesis with various
improvements over the earlier Ball '673 device. FIG. 4 shows one
example of such an implantable hearing prosthesis 400 having a
silicone elastomer receiver housing 401 (e.g., about 4.5 mm thick)
that contains a receiving coil 402 and a holding magnet 403.
Implant signal processor 404 receives the communications signals
from the receiving coil 402 and produces a corresponding electrical
stimulation signal to a bone conduction transducer 405, which is a
dual opposing magnet type floating mass transducer (FMT). The FMT
mass of the bone conduction transducer 405 is enclosed in a
titanium transducer housing 406, which typically may be about 17 mm
across and about 11 mm in depth.
[0027] FIG. 5 shows various internal structural details of a bone
conduction transducer 500 for an implantable hearing prosthesis 400
as shown in FIG. 4. An axially central electromagnetic coil 501 is
surrounded by a coil spacer 513, a central base core 504, and core
spacer 506. The central base core 504 and core spacer 506 are made
of soft iron that increases the magnetic coupling of the magnetic
field to provide a magnetic conduction path for the coil flux.
Radially surrounding central core subassembly is a moveable
subassembly of one or more ring-shaped permanent magnets 502
assembled together with a soft iron magnet carrier 503 and one or
more magnet spacers 512. This moveable subassembly is attached to a
top suspension subassembly of a top membrane spring 505 together
with a soft iron top lid 507, and a bottom suspension subassembly
of a bottom membrane spring 509 together with a soft iron bottom
lid 508. The bias point of the permanent magnets 502 can be kept in
a safe range (high B-field, low H-field) with respect to
demagnetization from aging or external magnetic fields.
[0028] Operation of the transducer 500 is based on employing a
motion constraint (e.g., the self-centering parallel membrane
springs 505 and 509) to create a linear-mode inertial drive of
electrical stimulation signals. The electrical stimulation signal
from the implant signal processor 404 is received by coil feeds 511
in a coil feed clip 510 and developed by the electromagnetic coil
501 and base core 504. This produces a coil magnetic field that
interacts with the base core 504, the one or more permanent magnets
502, and magnet carrier 503. The one or more permanent magnets 502
and magnet carrier 503 vibrate in response to the stimulation
signal. This vibration of the transducer 500 is then coupled to the
adjacent bone for bone conduction to the cochlea.
[0029] In addition, the arrangement of structural features in the
transducer 500 avoids magnetic short circuits due to the air gaps
between the moveable permanent magnets 502 and the non-moveable
electromagnetic coil 501 and core spacer 506. The non-magnetic
membrane springs 505 and 509 prevent these air gaps from collapsing
when the transducer 500 is excited by an electrical stimulation
signal (one of the moveable parts would magnetically stick to one
of the core parts). Instead, when there is no stimulation signal,
the forces in the air gaps generated by the magnetic bias flux
compensate and balance each other. When an electrical stimulation
signal is present and providing excitation to the transducer 500,
the flux density will weakened in one of the air gaps and boosted
in the other. The resulting net force is non-zero and the moveable
subassembly moves in response. Vice versa, the transducer 500 can
be used to generate a corresponding electrical signal from
vibrational excitation, for example, to act as an implant sensor or
to generate energy for the implant system. Closed-loop control
applications may be realized by fitting the transducer 500 with a
sensing element.
[0030] Inductance can be minimized in the electromagnetic coil 501
by controlling stray magnetic flux. Mechanical resonance frequency
of the transducer 500 also can be fine-tuned in various ways such
as by spring trimming with a cutting laser. Eddy currents can be
used in the transducer 500 to provide dampening of resonance peaks
by magnetically non-conductive short circuit elements. Some
embodiments may also immerse components in a viscous fluid for
additional dampening.
[0031] Compared to prior inertial transducers, the transducer 500
in FIG. 5 better maximizes the inertia of the involved masses (and
also thereby achieving lower resonance frequencies) by having the
moveable subassembly of the permanent magnets 502 and magnet
carrier 503 radially outside the electromagnetic coil 501 and
central base core 504. Similarly, having loss-generating components
such as the electromagnetic coil 501 closer to the axial center of
the transducer 500, higher efficiency is enjoyed as compared to
prior art arrangements.
[0032] Such an arrangement is also easily manufacturable because of
the rotationally symmetric design, use of relatively massive
non-laminated yoke components with low electrical conductivity. In
addition, it may be useful to use multiple separate yoke parts
and/or use components with self-centering characteristics. Radial
slots in one or more of the yoke components may also be useful for
minimizing the influence of eddy currents. Such an arrangement also
minimizes distortion compared to prior art designs by intentionally
introducing ferromagnetic saturation in certain yoke regions by
stabilizing constant bias flux. Besides use for bone conduction
hearing applications, a transducer 500 may be useful in other types
of applications such as for bone healing, a membrane pump, energy
harvesting, active vibration dampening, hydraulic valves,
loudspeakers, and/or vibration exciter.
[0033] Returning to FIG. 4, the receiver housing 401 and the
transducer housing 406 are connected at an unbiased pivot point
408. The unbiased pivot point 408 allows the receiver housing 401
to be bent out of the plane containing the upper surface of the
transducer housing 406 so that it lies correctly in a relaxed
condition in proper position under the skin, without the kind of
undesirable bias force found in the devices described in Ball '863
that tends to flex the receiver housing back towards the plane of
the transducer housing. Such unbiased bending of the housings
relative to each other is helpful for accommodating different sizes
of patient skulls and corresponding varying amounts of skull bone
curvature. Some skulls are relatively smaller and therefore need
relatively more bend between the housings, while other skulls are
relatively larger and little or no bending of the housings may be
needed. In one specific embodiment, the receiver housing 401 can be
bent without residual biasing force up to 180 degrees from a 90
degree superior to a 90 degree inferior position in relation to the
transducer housing 406.
[0034] Mounting of the transducer housing 406 to the skull bone is
accomplished by two single mounting points 407 which are opposite
to each other on the outer perimeter of the transducer housing 406
so as to couple the mechanical vibration signal from the bone
conduction transducer 405 via bone conduction to the cochlea. The
use of two single mounting points 407 in the implantable hearing
prosthesis 400 avoids some of the bone planarity issues associated
with the multiple mounting point embodiments described in Ball
'673. The mounting points 407 may be secured to the skull bone with
single-use self-tapping bone screws, e.g., 6-8 mm in length. Use of
self-drilling screws may cause micro-fractures in the bone. In some
patients, it may be preferred to use different length bone screws
in each mounting point 407.
[0035] An implantable hearing prosthesis 400 can be implanted in a
relatively simple surgical procedure that may take as little as 30
minutes. The surgeon creates a skin incision over the desired
location of the device, a bone bed is prepared, and screw holes are
pre-drilled for the mounting screws. An implant template may be
useful for these steps to aid in preparation of the proper size and
shape bed and/or to act as a drill guide for drilling of the screw
holes. The hearing prosthesis 400 is inserted into position and
secured with the mounting screws which are tightened to a defined
torque. Then the receiving housing 401 is bent into proper position
at the unbiased pivot point 408, and the incision is closed.
[0036] FIG. 6A-C shows various views of one specific embodiment of
a bone conduction transducer 600 for an implantable hearing
prosthesis which uses one or more piezoelectric members 606. Signal
input 603 is a feed-through wiring arrangement that receives an
electrical stimulation signal from an implant signal processor. A
transducer housing 601 is suspended below the piezoelectric members
606 in a prepared bone recess which surrounds the inertial mass
housing 601. The piezoelectric members 606 respond to the
electrical stimulation signal with corresponding mechanical
vibrations. The mechanical vibrations are also imparted to the
transducer housing 601 that is suspended below the piezoelectric
members 606 and in effect amplifies the magnitude of the mechanical
vibrations. The mechanical vibrations of the transducer housing 601
and the piezoelectric members 606 are coupled through mounting
points 606 and corresponding connecting screws 604 which attach to
the skull bone (such as the cortical bone or the temporal bone of
the patient), and carried by bone conduction to the cochlea to be
perceived as sound.
[0037] FIG. 7A-E shows various views of another embodiment a bone
conduction transducer 700 of an implantable hearing prosthesis
based on an inertial mass housing arrangement which includes one or
more electromagnetic coils 704 surrounding a permanent magnet 701
for responding to the electrical stimulation signal with the
corresponding mechanical vibrations. In this case, the
electromagnetic coils 704 are contained in a hermetic cylindrical
coil housing 702 made of titanium within which is the inertial mass
of the permanent magnet 701. The permanent magnet 701 is flexibly
suspended within the center of the coil housing 702 by a flexible
connector member 706. In the example shown, the flexible connector
member 706 is in the specific form of arcuate segments of a
flexible diaphragm.
[0038] Operation of this embodiment can most clearly be seen from
the view shown in FIG. 6E. The electromagnetic coils 704 respond to
the electrical stimulation signal with a varying electromagnetic
field that in turn interacts with the permanent magnet 701 to
generate corresponding mechanical vibration that moves the
permanent magnet 701 up and down. The mechanical vibrations are
coupled through the flexible connector member 706 to the coil
housing 702 to the mounting points 705 and corresponding connecting
screws 707 which attach to the skull bone (such as the cortical
bone or the temporal bone of the patient). The skull bone then
conducts the audio information of the mechanical vibrations to the
cochlea.
[0039] FIG. 8A-C shows various views of another embodiment of the
present invention. An external processor 810 contains one or more
sensing microphones for sensing the acoustic environment around a
patient user and generating a corresponding microphone signal. From
the microphone signal the external processor generates a
representative communication data signal which is transcutaneously
transmitted by an external transmitting coil 808 to an implanted
receiving coil 802. An implant magnet 803 within the receiving coil
802 magnetically interacts with a corresponding external holding
magnet 809 within the transmitting coil 808 to hold the external
processor 810 in a correct position. An implantable signal
processor 804 converts the communication data signal from the
receiving coil 802 into a representative electrical stimulation
signal. An implantable transducer housing 806 is fixedly attachable
to the skull bone 801 of the patient. An implantable drive
transducer 805, in this case an electromagnetic drive coil, is in
communication with the signal processor 804 and removably
engageable with the transducer housing 806 for applying to the
transducer housing 806 a mechanical vibration signal based on the
electrical stimulation signal for audio perception by the
patient.
[0040] In the embodiment shown in FIG. 8, transducer housing 806 is
fixedly attached to the skull bone 801 during a surgical procedure
such as the one shown in FIG. 9A-C. In FIG. 9A, a surgical incision
901 is made in the patient's skin around the site of the transducer
housing 806 behind the ear auricle 903. Retractors 902 pull back
the skin and ear auricle 903 from the surgical site to provide
access for a surgical drill 904 to prepare a recessed bone well in
the skull bone 801. The transducer housing 806 is then fixed in
place in the bone wells by a pair of radially opposed bone screws
807, after which the remainder of the prosthetic system is
implanted including inserting the drive transducer 805 into the
ready transducer housing 806. Then later, if any portion of the
system needs replacement, the drive transducer 805 can be easily
withdrawn from the transducer housing 806 during a simple surgical
procedure without disturbing the existing connection with the
patient skull bone 801.
[0041] FIG. 10A-C shows an embodiment of an implantable prosthesis
system 1000 wherein a silicone elastomer mold 1001 encases an
electromagnetic drive coil 1005 (e.g., made polyimed coated gold
wire) together in a sealed engagement with a low-profile transducer
housing 1006. The silicone elastomer mold 1001 provides protective
encasing of the drive coil 1005 and may also act as a spring to
enhance long term stability and reduce signal distortion. The
low-profile transducer housing 1006 includes a drive magnet 1008
which interacts with the electromagnetic drive coil 1005 to couple
the mechanical vibration signal to the underlying skull bone. FIG.
10C shows a variation in which the drive magnet 1008 has a coaxial
double magnet arrangement where the center has a first magnetic
polarity and the outer ring has a second opposite magnetic
polarity. In this embodiment, the drive coil 1005 may be arranged
correspondingly, for example, in a tight central structure that
interacts mainly with the center of the drive magnet 1008.
[0042] FIG. 11A-B shows embodiments having different height
profiles on the transducer housing 1106. In both embodiments, the
transducer housing 1106 forms a hermetically sealed can, but in the
embodiment shown in FIG. 11A, the transducer housing is much
higher, e.g., about the same as the diameter of the housing,
typically around 10 mm. FIG. 11B shows a lower height transducer
housing 1106 which has a height much less than the diameter of the
housing, e.g., about 5 mm. Where the height of the transducer
housing 1106 is higher such as shown in FIG. 11A, it is more likely
that a recessed bone well may be needed where the housing is fixed
the skull bone in order to accommodate the relatively high profile
of the housing. On the other hand, where the height of the
transducer housing 1106 is lower as shown in FIG. 11B, it may be
that the housing can be correctly attached to the skull bone with
needing a recessed bone well, thereby making surgical installation
much easier.
[0043] In some embodiments, the drive transducer may be a
piezoelectric transducer. For example, FIG. 12A shows an embodiment
of a drive transducer 1200 having an inertial mass 1201 that is
coupled to a piezoelectric stack 1205 containing piezoelectric
elements stacked parallel to the surface of the skull bone. In this
embodiment, a coupling bow 1202 of stiff material (e.g., titanium)
provides the mechanical connection of the inertial mass 1201 to the
piezoelectric stack 1205.
[0044] FIG. 12B shows an embodiment where the drive transducer 1200
includes opposing inertial masses 1201 at either end of a
piezoelectric stack 1205 containing piezoelectric elements stacked
perpendicular to the surface of the skull bone. A coupling
diaphragm 1203 of stiff material (e.g., titanium) mechanically
connects the drive transducer 1200 to the skull bone. FIG. 12C
shows another embodiment where the drive transducer 1200 includes a
single inertial mass 1201 at one end of a piezoelectric stack 1205
containing piezoelectric elements stacked perpendicular to the
surface of the skull bone.
[0045] In some embodiments, shown for example in FIG. 13A-B, the
drive coil 1301 may be covered by an encapsulation layer 1302 of
biocompatible material such as silicone or acrylic. In the specific
embodiments shown in FIG. 13A-B, the outer axial end of the drive
coil 1301 has a sealing lens 1300 of biocompatible material which
helps with the installation of the drive coil 1301 in the
transducer housing. Such a sealing lens 1300 may also act as a
spring to help minimize signal distortion. The sealing lens 1300 in
FIG. 13B also includes a separate coupling spring 1303 incorporated
into the encapsulation layer 1302 at the inner axial end of the
drive coil 1302 for coupling the drive coil 1302 to the transducer
housing with minimal distortion and long term durability. In other
embodiments, the transducer housing may include such a coupling
spring.
[0046] Embodiments of the present invention may be most appropriate
for patients with conductive hearing impairment exhibiting mixed
hearing loss with bone conduction thresholds better than or equal
to 45 dB HL at various audiogram evaluation frequencies. A
physician considering use of such a device should fully assess the
potential risks and potential benefits for the patient, bearing in
mind the patient's complete medical history, and exercising sound
medical judgment. Embodiments may be contraindicated for patients
with an existing mastoid condition that precludes attachment of the
transducer, patients with retrocochlear or central auditory
disorders, and/or patients with any known allergies to any of the
materials used in the device.
[0047] Although various exemplary embodiments of the invention have
been disclosed, it should be apparent to those skilled in the art
that various changes and modifications can be made which will
achieve some of the advantages of the invention without departing
from the true scope of the invention.
* * * * *